I have only had true blocks with the ostomy but I too thought I was experiencing a blockage with the j pouch twice when the gas became horrific and there was no output for hours. Both eventually passed and I think it was indeed gas. My go-to for all intestinal woes these days is chewable ginger which are indicated for nausea but I find they help me a great deal. Sometimes I wonder if it's a bit of a placebo, but really, do I care? There was no question with the ostomy blockages. They would always start with upper stomach gas but then the vomiting would begin.
I hope you find relief. I often find pain scary.